How to calculate external capacitor value
from required hold-up time?

1. Requirement of the extension of hold-up time

The demand for the longer hold-up time is increasing in order to keep output voltage during the instantaneous interruption. Adding a smoothing capacitor enables to extend hold-up time (Th), and adding output capacitor enables to extend fall time(Tf).

2.Extension method of hold-up time

1) In the case of AC-DC converter

It is necessary to increase the capacitance of smoothing capacitor on primary side to extend hold-up time.
The TU series have design flexibility and hold-up time can be extended by adding a smoothing capacitor externally.
In LFP240F/300F, the external capacitor unit is available as optional parts (available only with -U1Y option).

2)In the case of DC-DC converter

It is necessary to add an external capacitor between +Vin and -Vin to extend hold-up time.

3.Calculation formula of required capacitance for hold-up time

External capacitor (Cbc) value can be calculated with following formula.

Calculation example
-Product: TUHS10F05
-Input voltage: 100Vac
-Output power: 4W
-Required hold-up time: 200ms
-Ambient temperature: -20ºC

1) Efficiency(η) and minimum input voltage for regulated output voltage(Vh) of TUHS10F05 are listed in test data.
    η:Efficiency (by Load Current) of P.4 at test data, at 100Vac, 0.8Aout, Efficiency is 80.6%.
    Vh:Minimum Input Voltage for Regulated Output Voltage of P.21 at test data, at 50%out, -20ºC,
        Minimum Input Voltage for Regulated Output Voltage is 38Vac.

2) Cbc value can be calculated by above formula.

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